Emissions control system and method

ABSTRACT

A system comprising a fuel converter comprising a catalyst composition capable of converting a fuel into a selected one or both of a syngas reductant and a short chain hydrocarbon reductant, wherein the catalyst composition comprises: cracking sites that perform a cracking function when a temperature of an exhaust fluid is greater than a predetermined threshold temperature, wherein the cracking function converts long chain hydrocarbon molecules to short chain hydrocarbon molecules; and partial oxidation sites that perform a catalytic partial oxidation function when the temperature of the exhaust fluid is less than the predetermined threshold temperature, wherein the catalytic partial oxidation function oxidizes the fuel to produce the syngas reductant; and a selective catalytic reduction catalyst reactor in fluid communication with the fuel converter and the exhaust fluid.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure includes embodiments that relate to systems for controlling emissions. The disclosure further includes embodiments that relate to a method for controlling emissions.

2. Discussion of Art

Some vehicles may emit nitrogen oxides (NO_(x)) during use. Such emissions may be undesirable.

Emission controls have included engine modification and exhaust gas treatment. It may be desirable to have a system for emissions control that differs from those systems currently available. It may be desirable to have a method of controlling emissions that differs from those methods that currently available.

BRIEF DESCRIPTION OF THE INVENTION

Disclosed herein are systems and methods for controlling emissions. In one embodiment, the method of controlling emissions includes a system comprising a fuel converter comprising a catalyst composition capable of converting a fuel into a selected one or both of a syngas reductant and a short chain hydrocarbon reductant, wherein the catalyst composition comprises: cracking sites that perform a cracking function when a temperature of an exhaust fluid is greater than a predetermined threshold temperature, wherein the cracking function converts long chain hydrocarbon molecules to short chain hydrocarbon molecules; and partial oxidation sites that perform a catalytic partial oxidation function when the temperature of the exhaust fluid is less than the predetermined threshold temperature, wherein the catalytic partial oxidation function oxidizes the fuel to produce the syngas reductant; and a selective catalytic reduction catalyst reactor in fluid communication with the fuel converter and the exhaust fluid.

A method for controlling emissions includes determining a measured temperature of an exhaust fluid; performing a catalytic partial oxidation of a fuel to a syngas reductant when the measured temperature is less than a predetermined threshold value, or converting a long chain hydrocarbon molecules into a short chain hydrocarbon reductant, in the presence of a catalyst composition, when the measured temperature is greater than the predetermined threshold value, reacting the syngas reductant and/or the short chain hydrocarbon reductant with the exhaust fluid in the presence of a selective catalytic reduction catalyst; and controlling a concentration of a component of the exhaust fluid based on the measured temperature.

The above described and other features are exemplified by the following Figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:

FIG. 1 is a schematic depiction of one exemplary embodiment of the system 10; and

FIG. 2 is a schematic depiction of one exemplary embodiment of a rotary fuel converter.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure includes embodiments that relate to systems and methods of controlling emissions. Systems and methods for controlling emissions may reduce the nitrogen oxides (NO_(x)) emissions from the exhaust stream of a vehicle or a stationary source. Vehicles may include, for example, locomotives, marine vessels, off-highway vehicles, tractor-trailer rigs, passenger vehicles, and the like. Emissions control refers to the ability to affect the compositional make-up of an exhaust gas stream. As exhaust gas is a mixture of components, the reduction of one component almost invariably increases the presence of another component. For clarity of discussion, the chemical reduction of NO_(x) is used as a non-limiting example of emission reduction insofar as the concentration of a determined species within the exhaust gas stream is controlled.

The system utilizes the fuel for the engine as a reductant to reduce NO_(x) emissions. The system converts the already on-board fuel into a broad range of reductants. The system advantageously utilizes short-chain hydrocarbons, hydrogen (H₂), and carbon monoxide (CO) obtained from a fuel conversion reactor to reduce NO_(x) emissions. The fuel converter converts fuel, for instance diesel fuel, into a hydrogen-rich syngas, short-chain hydrocarbons, which can include small amounts of H₂ and CO present as by-products, or some combination of the two. These are mixed with the exhaust stream and facilitate a reduction of NO_(x) emissions in the presence of a hydrocarbon based selective catalytic reduction (SCR) catalyst bed. The short-chain hydrocarbons and/or the hydrogen-rich syngas generated in-situ from the fuel converter will react with the NO_(x) in the exhaust stream and reduce NO_(x) to nitrogen at the surface of a selective catalytic reduction (SCR), thereby reducing NO_(x) emissions from the vehicle. The system can be advantageously utilized on board in all types of vehicles that employ internal combustion engines powered by hydrocarbon-based fossil fuels or isolated units that have no access to other reductants. The system can also be utilized on board in all types of locomotives that employ engines and turbines powered by hydrocarbon-based fossil fuels. In one embodiment, the hydrocarbon-based fossil fuels are liquids. In particular, the system can be utilized in vehicles that employ diesel engines. Locomotives that employ diesel engines and diesel turbines can use the system on board for reduction of NO_(x) emissions. The system can be also utilized in stationary combustion sources burning hydrocarbon-based fuels. The system described herein does not require the need for additional reductant chemicals or the storage equipment required to be on-board therewith.

The system converts the already on-board fuel into a broad range or reductants by utilizing a fuel converter that can operate in a auto-thermal cracking (ATC) mode, a catalytic partial oxidation (CPO) mode, or a combination thereof. The flexibility of operating between these two modes can generate either short chain hydrocarbon reductants (i.e., light hydrocarbons) in the ATC mode, or hydrogen-rich syngas via the CPO mode. All of the reductants can be produced from the fuel on board. The flexible design of the fuel converter is a result of the catalyst composition disposed therein. The catalyst composition is capable of converting the on-board fuel into a selected one or both of the hydrogen-rich syngas reductant and the short chain hydrocarbon reductant. The catalyst composition includes cracking sites that perform a cracking function when a temperature of an exhaust fluid is greater than a predetermined threshold temperature, wherein the cracking function converts long chain hydrocarbon molecules to short chain hydrocarbon molecules. The catalyst composition further includes oxidation sites that perform a catalytic partial oxidation function when the temperature of the exhaust fluid is less than the predetermined threshold temperature, wherein the catalytic partial oxidation function oxidizes the fuel to produce the hydrogen-rich syngas reductant. In one embodiment, the predetermined threshold temperature is about 150 to about 400 degrees Celsius

With reference now to FIG. 1, an example of system 10 for the reduction of NOx emissions comprises a fuel tank 12, a fuel converter 14, a SCR catalyst reactor 16 and an engine 18. The fuel tank 12 is upstream of the fuel converter 14 and the SCR catalyst reactor 16. The fuel tank 12, the fuel converter 14, and the SCR catalyst reactor 16 are in fluid communication with one another. The fuel converter 14 is located between the fuel tank 12 and the SCR catalyst reactor 16 and is upstream of the SCR catalyst reactor 16. The engine 18 is located downstream of the fuel tank 12 and in fluid communication with the fuel tank 12. The engine is located upstream of the fuel converter 14 and the SCR catalyst reactor 16 and is in fluid communication with both the fuel converter 14 and the SCR catalyst reactor 16.

The system 10 can also employ two optional separators—a first separator 20 and a second separator 22. The optional separators 20 and 22 comprise distillation columns (with optional vacuum systems), packed columns, membranes, condensers, centrifuges, or the like that can be used to separate aromatics from paraffins or long-chain hydrocarbons from the short-chain hydrocarbons. In one embodiment, aromatics are separated from the hydrocarbons in the separator 20, while heavy hydrocarbons are separated from the short-chain hydrocarbons in the separator 22. The heavy hydrocarbons are recycled to the fuel tank 12 so that they can be consumed in the engine 18.

In one embodiment, the system 10 can further comprise a controller 23 operable to control a flow of the exhaust fluid to the fuel converter 14. As will be described in greater detail below, the controller 24 can permit the flow of the exhaust fluid to the fuel converter 14 when the temperature of the exhaust fluid is less than a predetermined threshold temperature. The system 10 can still further include a second controller 24, which is operable to control the flow of fuel to the fuel converter 14, and thus control the production of the syngas reductant and/or the short-chain hydrocarbon reductant.

The term “fluid communication” encompasses the containment and/or transfer of compressible and/or incompressible fluids between two or more points in the system 10. Examples of suitable fluids are gases, liquids, combinations of gases and liquids, or the like. The use of pressure transducers, thermocouples, flow, hydrocarbon, NOx sensors aid in communication and control. In one embodiment, computers can be used to aid in the flow of fluids in the system. The term “on-board” refers to the ability of a vehicle or locomotive to host the system 10 in its entirety aboard the vehicle or locomotive.

A variety of fuels may be stored in the fuel tank 12 and used in the system 10. In one embodiment, the fuel is a hydrocarbon-based fossil fuel. It is desirable for the hydrocarbon-based fossil fuel to be a liquid. Examples of suitable liquids are diesel, gasoline, jet-fuel, logistic fuel (JP-8), kerosene, fuel oil, bio-diesel, or the like, or a combination comprising at least one of the foregoing hydrocarbon-based fossil fuels. As will be discussed in further detail below, the fuel converter 14 converts long-chain hydrocarbons to short-chain hydrocarbons which are then used to reduce NOx in the exhaust. Long-chain hydrocarbons are hydrocarbons that have 9 or more carbon atoms. In an exemplary embodiment, an exemplary long-chain hydrocarbon is diesel. Short-chain hydrocarbons are those that have 8 or less carbon atoms. Exemplary short-chain hydrocarbons are those having about 2 to about 8 hydrocarbons. Short-chain hydrocarbons are also termed paraffinic hydrocarbons. Paraffinic hydrocarbons can be saturated or unsaturated.

As mentioned above, the fuel converter 14 comprises a fixed bed reactor that comprises a catalyst composition. It is desirable for the catalyst composition to be able to operate under conditions that vary from oxidizing at the inlet of the reactor to reducing conditions at the exit of the reactor. The catalyst should be capable of operating effectively and without any thermal degradation from a temperature of about 200 to about 900° C. The catalyst should operate effectively in the presence of air, carbon monoxide, carbon dioxide, water, alkanes, alkenes, cyclic and linear compounds, aromatic hydrocarbons and sulfur-containing compounds. The catalyst composition should provide for low levels of coking such as by preferentially catalyzing the reaction of carbon with water to form carbon monoxide and hydrogen thereby permitting the formation of only a low level of carbon on the surface of the catalyst. The catalyst composition should be able to resist poisoning from such common poisons such as sulfur and halogen compounds. Moreover, an exemplary catalyst composition may satisfy all of the foregoing requirements simultaneously.

In one embodiment, the catalyst composition contained in the fuel converter 14 is bifunctional, i.e., it serves to crack heavier hydrocarbons to light hydrocarbons, while simultaneously preventing poisoning of the catalyst composition from coke depositions. Coke build-up that occurs during the cracking of hydrocarbons while using traditional zeolite cracking catalysts during processes such as fluidized catalytic cracking (FCC) deactivates the catalyst. The bifunctional catalyst advantageously slows down coke build-up rate on the surface of cracking catalysts, thus allowing it to continue being active for cracking hydrocarbons, which would normally not occur on conventional cracking catalysts operating under similar conditions.

In the catalyst composition, since the catalytic partial oxidation reaction is an exothermic reaction, while cracking is an endothermic reaction, the heat generated at a catalytic partial oxidation site facilitates the endothermic cracking reaction and also facilitates the oxidation of coke. In one embodiment, the catalytic partial oxidation sites are used to oxidize the coke away from the cracking sites to keep the cracking sites clean and active.

The use of a fuel converter 14 that employs the catalytic composition is advantageous in that it may use only a single fixed bed reactor to convert diesel fuel to a mixture of short-chain hydrocarbons and hydrogen-rich syngas. This mixture of short-chain hydrocarbons and syngas can be used as a reducing agent for NOx reduction in diesel engine exhaust and will be discussed later. If desired, the fuel converter can employ more than one fixed bed reactor to improve productivity. For example, the catalytic converter can employ about 2 to about 6 fixed bed reactors if desired.

The catalytic partial oxidation sites generally comprise noble metals that perform the catalytic partial oxidation function. The catalytic partial oxidation sites comprise one or more “platinum group” metal components. As used herein, the term “platinum group” metal implies the use of platinum, palladium, rhodium, iridium, osmium, ruthenium or mixtures thereof. Exemplary platinum group metal components are rhodium, platinum and optionally, iridium. The catalyst composition generally comprises about 0.1 to about 20 wt % of the platinum group metal. The platinum group metal components may optionally be supplemented with one or more base metals, particularly base metals of Group VIII, Group IB, Group VB and Group VIB of the Periodic Table of Elements. Exemplary base metals are iron, cobalt, nickel, copper, vanadium and chromium.

The cracking sites generally comprise a zeolite. The zeolites generally have a silica-to-alumina mole ratio of at least about 12. In one embodiment, a zeolite having a silica-to-alumina mole ratio of about 12 to about 1000 is used. In one embodiment, a zeolite having a silica-to-alumina mole ratio of about 15 to about 500 is used. Examples of suitable zeolites are RE-Y (rare earth substituted yttria), USY (ultrastable yttria zeolite), RE-USY ZSM-5, ZSM-11, ZSM-12, ZSM-35, zeolite beta, MCM-22, MCM-36, MCM-41, MCM-48, or the like, or a combination comprising at least one of the foregoing zeolites.

Zeolites also contemplated for use in this process are the crystalline silicoaluminophosphates (SAPO). Examples of suitable silicoalumino-phosphates include SAPO-11, SAPO-34, SAPO-31, SAPO-5, SAPO-18, or the like, or a combination comprising at least one of the foregoing silicoaluminophosphates.

The platinum group catalysts along with other base metal catalysts are washcoated onto the molecular sieves to form the catalytic composition. In one embodiment, the catalytic partial oxidation sites comprise about 0.1 to about 5.0 weight percent (wt %) of the total weight of the catalytic composition. In a preferred embodiment, the catalytic partial oxidation sites comprise about 0.3 to about 1.0 wt % of the total weight of the catalytic composition.

In one embodiment, the bifunctional catalyst composition of the fuel converter can comprise a combination of metals forming a uniform phase, such as trimetallic catalysts. An exemplary trimetallic catalyst is rhodium-platinum-iridium in proper stoichiometry to aid catalyst phase uniformity.

Catalyst supports may comprise alumina, titania, zirconia, ceria, silicon carbide or any mixture of these materials. Typically, the catalyst support comprises gamma-alumina with high surface area comprising impurities of at least about 0.2% by weight in one embodiment and at least about 0.3% by weight in another embodiment. The catalyst support may be made by any method known to those of skill in the art, such as co-precipitation, spray drying or sol-gel methods for example. The catalyst substrates can be foam, metal foil, fibrous metal, monolith, and the like. The substrates can be wash coated with the metal oxides before dispersion of, for example, the trimetallic catalyst composition onto the substrate.

A refractory support can further be included with the bifunctional catalyst composition to enhance stability of catalytic partial oxidation sites when sulfur and steam are present in a feed stream to the fuel converter.

Further, promoters can be used to enhance the dispersion of the trimetallic catalyst composition on the substrate. Exemplary promoters can include, without limitation, rhenium, rhodium, palladium, ruthenium, iridium, platinum, lanthanum, cerium, chromium, oxides thereof, and a combination comprising at least one of the foregoing.

In one embodiment, the trimetallic catalyst composition system comprises 0.2 wt % rhodium, 0.2 wt % iridium, and 0.3 wt % platinum, based on a total weight of the catalyst composition, dispersed on an alumina foam support washcoated with 5 wt % cerium, 0.5 wt % zirconium, and 0.01 wt % yttrium alumina.

In another embodiment, a wash-coated support substrate with a doped alumina wash coat can be used in order to maintain a gamma alumina phase of the composition, rather than the alpha alumina phase. Such an example could be chromium-europium doped alumina that is then wash coated onto a support. Chromium can form a Sapphire support substrate structure and europium can form defects within that structure. These crystals can then stabilize the overall structure of alumina into the gamma phase, thereby increasing catalyst stability.

In an exemplary embodiment, in one method of operating the fuel converter 14, a gas-assisted nozzle is utilized to atomize the fuel at a low-pressure inlet into the fuel converter 14 (not shown). The fuel, which primarily comprises heavy hydrocarbons undergoes cracking to form the short hydrocarbons. The short hydrocarbons are then used to reduce the NOx emitted in the engine exhaust. The reduction of the NOx with the short hydrocarbons occurs in the presence of an SCR catalyst as will be detailed later.

A portion of the hot exhaust gas that is emitted by the locomotive engine can be used as a secondary gas for atomizing the fuel. Air can also be employed as the secondary gas for atomizing the fuel. In an exemplary embodiment, a portion of the exhaust stream is combined with air to form the secondary gas to facilitate the catalytic partial oxidation reaction. The amount of hot engine exhaust gas is effective to light off the catalytic partial oxidation reaction in the fuel converter 14. The heat released from the exothermic catalytic partial oxidation reaction will drive the endothermic cracking reaction forward. Water present in the exhaust stream can facilitate the reduction of coke formation on the catalyst.

In one embodiment, in order to light off the catalytic partial oxidation reaction, the oxygen/carbon (O2/C) mole ratio in the feed gas that is supplied to the fuel converter is in an amount of about 0.01 to about 0.5. In another embodiment, the oxygen/carbon (O2/C) mole ratio in the feed gas is in an amount of about 0.05 to about 0.4. In yet another embodiment, the oxygen/carbon (O2/C) mole ratio in the feed gas is in an amount of about 0.1 to about 0.3. An exemplary (O2/C) mole ratio in the feed gas is in an amount of about 0.1.

The temperature of the fuel converter is maintained at about 550° C. to about 650° C., during the conversion of long-chain hydrocarbons to short-chain hydrocarbons. In one embodiment, the temperature of the fuel converter is maintained at about 580° C. to about 640° C., during the conversion of long-chain hydrocarbons to short-chain hydrocarbons. An exemplary temperature is about 600 to about 620° C. At about 600 to about 620° C., the deposition of sulfate groups derived from sulfur containing organic compounds will be reduced and hence the sulfur tolerance of the system 10 is enhanced.

If coke species accumulate on the catalyst composition in the fuel converter during the catalytic partial oxidation process, the flow rate of engine exhaust gas (which contains considerable quantity of oxygen and water) can be periodically increased to burn and steam the coke off and to regenerate the hybrid catalyst activity. A single valve (not shown) can also periodically be used to increase the flow rate of engine exhaust gas and/or air to burn the coke off.

In one embodiment, in order to burn off coke that is deposited on the catalytic composition, the O2/C mole ratio in the feed gas to the diesel converter can be varied in an amount of about 0.1 to about 0.75. In one embodiment, in order to burn off coke that is deposited on the catalytic composition, the O2/C mole ratio in the feed gas to the diesel converter can be varied in an amount of about 0.2 to about 0.55. An exemplary O2/C mole ratio in the feed gas to the diesel converter is about 0.5.

The temperature of the fuel converter is maintained at about 550° C. to about 750° C., during the burning off coke that is deposited on the catalytic composition. In one embodiment, the temperature of the fuel converter is maintained at about 600° C. to about 720° C., during the burning off coke that is deposited on the catalytic composition. In another embodiment, the temperature of the fuel converter is maintained at about 620° C. to about 710° C., during the burning off coke that is deposited on the catalytic composition. An exemplary temperature is about 650 to about 700° C. during the burning off coke that is deposited on the catalytic composition.

The use of the catalytic composition in conjunction with an increased exhaust gas and/or air flow to burn off the coke is advantageous in that it overcomes the need for a system comprising two reactors to perform the cracking and regeneration functions. Noble metals such as rhodium, iridium and platinum are also oxidation catalysts, and they will also help to burn the coke more efficiently off the zeolite cracking catalyst. The noble metal promotes oxidation of coke into carbon dioxide and minimizes or completely avoids formation of carbon monoxide during the coke oxidation process.

In another embodiment, in another method of operating the fuel converter 14, the fuel converter 14 can comprise a rotary reactor, wherein the inlet port of such a reactor can be periodically rotated through a first small angle. FIG. 2 is an exemplary embodiment or a rotary reactor 100 that can be used as a fuel converter. The rotary reactor 100 comprises 4 reaction chambers 102, 104, 106, and 108 each of which contains the catalyst composition. Each reaction chamber also comprises an inlet port 110 that is used to permit feed gases into the reactor. The chambers and the inlet ports can be rotated about a shaft 112.

The rotation of the inlet port can be conducted automatically via a computer. By rotating the inlet port of the reactor, a small portion of the reactor can be subjected to the high temperature exhaust gases. The coke disposed upon the catalyst composition contained in this small portion of the reactor is oxidized by the hot exhaust gases and removed. Thus a small portion of the catalyst composition is completely regenerated, and the inlet port can be rotated through a second small angle in order to regenerate another portion of the catalyst. The rotation can be continued throughout the process to continuously convert long-chain hydrocarbons to short-chain hydrocarbons and syngas without significant catalyst deactivation due to coking. As noted above, syngas comprises hydrogen and carbon monoxide, both of which are useful reducing agents when exhaust gases having a low temperature are used. The use of the continuously operating fuel converter 14 permits it to be used on-board in vehicles and locomotives.

The short-chain hydrocarbons obtained from the fuel converter 14 are then permitted to flow to the SCR catalyst reactor 16, where they are used to reduce the NOx in the engine exhaust stream. The reduction of NOx occurs over a selective catalytic reduction catalyst. Examples of suitable selective catalytic reduction catalysts are metals such as silver, gallium, cobalt, molybdenum, tungsten, indium, bismuth, vanadium or a combination comprising at least one of the foregoing metals in a binary, ternary or quaternary mixture disposed upon a suitable support. Oxides of metals can be used as catalysts if desired. Oxides of metals can also be used as catalyst supports. Examples of suitable metal oxide supports are alumina, titania, zirconia, ceria, silicon carbide, or a combination comprising at least one of the foregoing supports.

The short-chain hydrocarbons can be used to reduce NO_(x) in the exhaust stream, according to the following overall reaction (1).

NO_(x)+O₂+organic reductant→N₂+CO₂+H₂O  (1)

The exhaust stream usually comprises air, water, CO, CO₂, NO_(x), SO_(x), H₂O and may also comprise other impurities. Water contained in the exhaust stream is generally in the form of steam. Additionally, uncombusted or incompletely combusted fuel may also be present in the exhaust stream. The short-chain hydrocarbon molecules comprising less than or equal to about 8 carbon atoms along with CO and H₂ is fed into the exhaust stream to form a gas mixture, which is then fed through the selective catalytic reduction catalyst. Sufficient oxygen to support the NO_(x) reduction reaction may already be present in the exhaust stream. If the oxygen present in the exhaust stream is not sufficient for the NO_(x) reduction reaction, additional oxygen gas may also be introduced into the exhaust stream in the form of air. In some embodiments the gas mixture comprises from about 1 mole percent (mole %) to about 21 mole % of oxygen gas. In some other embodiments the gas mixture comprises from about 1 mole % to about 15 mole % of oxygen gas.

The NO_(x) reduction reaction may take place over a range of temperatures. In one embodiment, the reduction reaction can occur at a temperature of about 200° C. to about 600° C. In another embodiment, the reduction reaction can occur at a temperature of about 300° C. to about 500° C. In yet another embodiment, the reduction reaction can occur at a temperature of about 350° C. to about 450° C.

If syngas is produced during the conversion of heavy hydrocarbons to short-chain hydrocarbons in the fuel converter 14, then reduction of NO_(x) in the SCR catalyst reactor 16 with the short-chain hydrocarbons and syngas can take place at temperatures of as low as about 150° C., according to the following reaction (2).

NO_(x)+H₂+CO+organic reductant→N₂+H₂O+CO₂  (2)

In one embodiment, reaction (2) occurs at a temperature of about 100 to about 500° C. In another embodiment, the reaction occurs at a temperature of about 150 to about 350° C. The system 10 detailed above provides many advantages that make it useful in diesel locomotives. The catalyst composition advantageously displays both a cracking function as well as a catalytic partial oxidation function. This reduces the need for a system having two reactors with multiple hot valves, which alternately switches between cracking and regeneration modes thereby reducing costs.

Additionally, the use of a simple air-valve to periodically increase the flow rate of engine exhaust gas and/or air to burn the coke off, also reduces the need for a system having two or more reactors. The use of the gas-assisted nozzle facilitates the atomization of the long-chain hydrocarbons such as diesel at a low pressure. In one embodiment, the fuel pressure is less than or equal to about 8 bar (8.15 kg/cm²) and the air pressure is less than or equal to about 6.5 bar (6.62 kg/cm²) prior to entry into the fuel converter 14. In one embodiment, the fuel pressure is less than or equal to about 6 kg/cm² and the air pressure is less than or equal to about 4.5 bar kg/cm² prior to entry into the fuel converter 14. In yet another embodiment, the fuel pressure is less than or equal to about 4.5 kg/cm² and the air pressure is less than or equal to about 3.5 bar kg/cm² prior to entry into the fuel converter 14.

In addition, the use of a fuel converter 14 that can rotate (i.e., functions as a rotary reactor) permits regeneration of the entire catalyst bed thereby permitting continuous operation. This allows for an effective on-board utility while reducing operating and maintenance costs.

The system 10 advantageously uses hot exhaust gases from the exhaust stream to light off the catalytic partial oxidation function of the catalyst composition. This permits integration of the system 10 with the exhaust system to improve the efficiency of the fuel converter 14. The use of hot exhaust gases advantageously facilitates the production of syngas, which can be used to reduce the NO_(x) concentration at lower temperatures. In addition, the hydrogen contained in the syngas minimizes coke formation.

Turning back now to FIG. 1, an optional separator 20 is located down stream of the fuel tank 12 and upstream of the fuel converter 14 and is in fluid communication with the fuel tank 12 and the fuel converter 14. A feed back loop between the first separator 20 and the fuel tank 12 serves to recycle heavy hydrocarbons species to the fuel tank 12 or engine 18. The first separator comprises distillation columns with optional vacuum systems, membranes, condensers, centrifuges, or combinations thereof that can be used to separate aromatic heavy hydrocarbons from the paraffinic short-chain hydrocarbons, and wherein the aromatics output from the first separator is recycled back to the fuel tank, and the paraffinic hydrocarbons are fed to the fuel converter.

An additional optional separator 22 can also be located between the fuel converter 14 and the SCR catalyst reactor 16. The second separator 22 is located down stream of the fuel converter 14 and upstream of the SCR catalyst reactor 16. The second separator 22 is in fluid communication with the fuel converter 14 and upstream of the SCR catalyst reactor 16. A feed back loop between the second separator 22 and the fuel tank 12 serves to recycle heavy hydrocarbons to the fuel tank 12 or engine 18. Separator 22 seeks to increase fuel efficiency and increase the robust nature of the SCR catalyst while separator 20 seeks to improve the reliability of the fuel converter and increase fuel efficiency. As noted above, the separators are optional. However, in one embodiment, either the first separator 20 or the second separator 22 can be used in the system. In yet another embodiment, both the first separator 20 and the second separator 22 can be used in the system. It is generally desirable to use the second separator due to its low cost and low fuel consumption. Additionally, the second separator 22 introduces more robustness to the system of producing a rich-stream in useful reductants to the SCR system.

In an exemplary embodiment, the second separator 22 can be a simple packed column e.g., a vessel with some packing material such as pall rings packed inside a column with either some coils or a jacket where cooling water at a temperature of about 70 to about 99° C. available on the locomotive will flow through and maintain the column temperature at about 100 to about 200° C. In another embodiment, a cooled knock-out plate or a condenser operating at a temperature of about 90 to about 150° C. with heated return lines can be used to return the heavy hydrocarbons to the fuel tank 12 or engine 18. This facilitates uniform viscosity and flow characteristics for the heavy hydrocarbons that are returned to the fuel tank 12 or the engine 18.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Ranges disclosed herein are inclusive and combinable (e.g., ranges of “up to about 25 wt %, or, more specifically, about 5 wt % to about 20 wt %”, is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt % to about 25 wt %,” etc.). “Combination” is inclusive of blends, mixtures, alloys, reaction products, and the like. Furthermore, the terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the colorant(s) includes one or more colorants). Reference throughout the specification to “one embodiment”, “another embodiment”, “an embodiment”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the invention belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims. 

1. A system comprising: a fuel converter comprising a catalyst composition capable of converting a fuel into a selected one or both of a syngas reductant and a short chain hydrocarbon reductant, wherein the catalyst composition comprises: cracking sites that perform a cracking function when a temperature of an exhaust fluid is greater than a predetermined threshold temperature, wherein the cracking function converts long chain hydrocarbon molecules to short chain hydrocarbon molecules; and partial oxidation sites that perform a catalytic partial oxidation function when the temperature of the exhaust fluid is less than the predetermined threshold temperature, wherein the catalytic partial oxidation function oxidizes the fuel to produce the syngas reductant; and a selective catalytic reduction catalyst reactor in fluid communication with the fuel converter and the exhaust fluid.
 2. The system of claim 1, further comprising an engine in fluid communication with a fuel tank and the selective catalytic reduction catalyst reactor, wherein the engine is located downstream of the fuel tank and upstream of the selective catalytic reduction catalyst reactor.
 3. The system of claim 1, further comprising a controller operable to control a flow of the exhaust fluid to the fuel converter.
 4. The system of claim 3, wherein the controller permits the flow of the exhaust fluid to the fuel converter when the temperature of the exhaust fluid is less than the predetermined threshold temperature.
 5. The system of claim 3, wherein the control of exhaust fluid flow is effective to change an oxygen to carbon molar ratio in the fuel in the fuel converter.
 6. The system of claim 1, further comprising a controller operable to control the flow of fuel to the fuel converter and thus control the production of the syngas reductant and/or the short-chain hydrocarbon reductant.
 7. The system of claim 1, wherein the cracking sites comprise a zeolite and the partial oxidation sites comprise a dispersed noble metal.
 8. The system of claim 1, wherein the catalyst composition comprises a platinum group metal dispersed on a catalyst support.
 9. The system of claim 8, wherein the platinum group metal comprises platinum, rhodium, palladium, iridium, osmium, ruthenium, or a combination comprising at least one of the foregoing.
 10. The system of claim 8, wherein the catalyst composition comprises about 0.1 weight percent to about 20 weight percent of the platinum group metal.
 11. The system of claim 9, wherein the platinum group metal further comprises one or more base metals from Group VIII, Group IB, Group VB or Group VIB of the Periodic Table of Elements.
 12. The system of claim 8, wherein the catalyst support comprises a monolith, wherein the monolith comprises foam, metal foil, fibers, or a combination comprising at least one of the foregoing.
 13. The system of claim 1, wherein the catalyst composition is trimetallic.
 14. The system of claim 13, wherein the trimettalic catalyst composition is rhodium-platinum-iridium in proper stoichiometry.
 15. The system of claim 13, wherein the catalyst composition further comprises a promoter configured to enhance the dispersion of the platinum group metal.
 16. The system of claim 15, wherein the promoter comprises rhenium, rhodium, palladium, ruthenium, iridium, platinum, lanthanum, cerium, chromium, gallium, or a combination comprising at least one of the foregoing.
 17. The system of claim 1, wherein the syngas reductant and/or the short-chain hydrocarbon reductant control a nitrogen oxide content of the exhaust fluid in the selective catalytic reduction catalyst reactor.
 18. A vehicle or stationary generator employing the system of claim
 1. 19. A locomotive employing the system of claim 1 on board.
 20. A method, comprising: determining a measured temperature of an exhaust fluid; performing a catalytic partial oxidation of a fuel to a syngas reductant when the measured temperature is less than a predetermined threshold value, or converting a long chain hydrocarbon molecules into a short chain hydrocarbon reductant, in the presence of a catalyst composition, when the measured temperature is greater than the predetermined threshold value; reacting the syngas reductant and/or the short chain hydrocarbon reductant with the exhaust fluid in the presence of a selective catalytic reduction catalyst; and controlling a concentration of a component of the exhaust fluid based on the measured temperature.
 21. The method of claim 20, wherein the converting occurs in a fuel converter, and wherein the fuel converter comprises a ratio of oxygen to carbon (O₂/C) in a range of from about 0.10 to about 0.75.
 22. The method of claim 20, wherein controlling the concentration comprises reducing a nitrogen oxide content in the exhaust fluid.
 23. The method of claim 20, further comprising regenerating the catalyst composition by diverting a portion of the exhaust fluid to the catalyst composition when the measured temperature is less than the predetermined threshold value. 